To increase the output and for the convenience of molding, a laminate plate 10 with a plurality of substrates 11, as shown in FIG. 1, is usually employed in the prior arts associated with molding process for electronic devices such as ICs. Each substrate 11 contains an electronic device package. There are several cutting troughs 12 between adjacent substrates, which facilitate the discrete substrates to be cut off after the molding process. There is a chip 13 located at the center area of each substrate. Several copper lines 14 surrounding the chip 13 on the substrate 10 are used to connect with the chip 13 by metallic lines 15. Finally, the substrate 11 undergoes the molding process by means of a suitable molding compound to form a molding body 17 enveloping the chip 13. A plurality of solder balls 16 are soldered on the back side of the substrate 10, as shown in FIG. 2.
The above-mentioned process is similar to one of the well-known molding methods for assembling the laminate plate and the molding compound, and easily releasing the runner and gate from the laminate plate, as disclosed in U.S. Pat. No. 5,635,761. There is a gold area 18 in each substrate deeply passing through the copper lines 14 at a desired corner of the substrate 11 close to the first pin which is defined by the prior arts, as shown in FIGS. 3 and 4.
During the molding process, the molding compound spreads over the laminate plate 10 along the gold area 18 to form a runner (or gate) 20 and the molding body 17. The runner 20 will be released from the laminate plate after a curing process for the molding compound. The gold area 18 essentially has low adhesion to the molding compound but the laminate plate typically has high adhesion such that the runner 20 can be easily released due to the difference in the adhesion property. However, the conventional molding process has several disadvantages as follows:
a. Gold, which is used to implement the gold area on the laminate plate, is so expensive that the cost is very high. PA0 b. The number of the output pins for the electronic device may be up to 64 or more than several hundreds. It is still difficult for the present technology to layout so many pins on the substrate. Due to the limited available area, each copper line 14 is designed to just be able to connect peripheral devices without further considering any electric effect resulting from the copper lines 14. The prior process requires a gold area to deeply pass into the copper lines 14 which occupy a portion of the available area of the substrate 11, and leads to the reduction of the number of the copper lines 14 as well as the increase in layout difficulty. PA0 c. Although the gold area 18 has low adhesion to the molding compound, it is still not low enough to completely release the runner 20 from the laminate plate 10 without any damage to the molding body. Thus, the molding body is sometimes released from the laminate plate which results in great reduction of the yield rate. It may also be possible that some molding compound remaining on the junction area of the gold area 18 and the molding body to ruin the appearance of the electronic device after the releasing process.
Apparently, the prior art process can not avoid damage to the molding body during the releasing process. It has become more and more desirable to improve the molding process and to prevent the molding body from being damaged or released from the substrate so as to increase the yield rate.